UPDATE - Help - electrical gremlins strike again

So short background story:

Went to Port Dover for Friday the 13th - all was well for the ride.
Went to leave PD - battery's dead... strange.
Battery is a new AGM type battery - new this past spring.
Manage to bump start it, got to the edge of town and it stalls. Won't start now for love nor money.
Not even enough power to make the solenoid click.
Bike comes home in the back of a truck. Charge the battery (intelligent battery charger - rated for AGM style) - takes about 18 hours to charge.

So finally get to doing some troubleshooting, and discovered something strange.
Battery in - starts and idles with no issues. Voltage at the battery is a little low -- lucky to get to 13.2 volts.

OK - manual says to move on to the alternator tests.
Check resistance of the 3 stator wires at the connector -- all in spec.
Check resistance of the 2 rotor wires at the connector - 40 ohms instead of 4. Houston, we have a problem.

Tear it apart.
Tested from each of the the connectors to it's associated brush (tested at the tip of the brush) - 0.5ohm each. Brushes are 17mm long - spec is at least 12. Hmmm ok. Tested the rotor itself - 4ohm. Also okay - that's odd.
Put it back together and test at the connector -- 122ohm now?
Loosen ever so slightly and wiggle the alternator cover with my hands - resistance jumps around between 35ohm to over 100ohm. Rotate the engine a few times, resistance numbers jump around, but never get any better than the 35ohm number, and it's still sensitive to the cover -- if I actually tighten it down it goes up to around 45ohm at best.
Haven't gotten as far as checking the voltage regulator/rectifier - but I was starting to suspect it until I found this.

So folks - how is this possible, and how do I fix it?

Greg

 

Well - no one replied here, but I solved it with some idea from over on the XJ Owners email list.

Commutator rings on the rotor were corroded and causing the increased resistance.

Polished them and the brush faces up with some 1000 grit sandpaper, then hit the copper rings with a dremel polishing bob and some chrome polish. Bright and shiny!

Tested, and the charging system is back to full power!

Just in case anyone else has this issue.

 

Tagged for later need possibly, Thanx Altus for posting what you had found to correct this.

 

Yes, very helpful indeed! I have been trying to resurrect an 81 XJ750 and ran into some odd numbers on the rotor.. had 10.2ohms.. so I am going to tear into that in the next week. I have a lot of stuff to accomplish yet before I can try and fire it up before the end of August though.

 

Sir, thankkkkkyoooouuuuuu! Ok, that was cornball enough so seriously, I have the same issue.

 

So I am following your lead and will be happy to post the results. Thanks a bunch for your follow up on this.

 

This has happened to my bike too battery going flat. I have almost 0 Ohms resistance in the stator tests. How do Icheck the brushes, has the text to be done with the brushes in contact with the rotor? I am getting continuity (with brushes not in contact with the rotor) when I put the voltmeter probe on one brush and one spade terminal ie green to green conducting current and brown to brown conducting current. The slip rings were dirty but I am wondering if I need to polish them more for the charging system to work. Evidently electrical systems are not my area of expertise.

 

stators very low resistance
specs in this link and trouble shooting charging system
The Ultimate Relay, Switch, Sensor, and Diodes Guide
Checking Alternator Stators:

Measure the resistance across each pair (white1 to white2, white1 to white3, and white2 to white3) of the three white wires (white1, white2, and white3) at the connector; the specifications should be:

0.50 ohms +/- 10% for all XJ550 models.

0.46 ohms +/- 10% for all XJ650, all XJ700, all XJ750, and XJ900RK models.

0.37 ohms +/- 10% for all XJ1100 models.

0.40 ohms +/- 10% for all XS1100 models.

Note that the resistance specifications for the stators are extremely small; they should barely have any resistance at all (compared to most other electrical devices).


Checking Alternator Rotors:

Measure the resistance across the two lead wires (usually brown and green) at the connector; the specifications should be:.

4.5 ohms +/- 10% for all XJ550 models.

4.0 ohms +/- 10% for all XJ650, all XJ700, all XJ750, XJ900RK, and XJ1100 models.

3.5 ohms +/- 10% for all XS1100 models (field coil).


Note that worn, dirty, or damaged alternator brushes can affect these readings, as can "dirty" copper commutator rings on the rotor face (where the brushes contact the rotor):

 

Hi XJ550H stator readings on my bike are 0.8 Ohms and all three wires are the same. There is no current flowing when I connect the multimeter between each white wire of the stator and the steel circular frame the stator is fixed to so I think the stator is fine. I assume I need to check the rotor resistances with the brush cover bolted to the crankcase?

 

yes with cover in place , you can measure across the copper if cover is off, but then you do not include the brushes and miss the chance to evaluate them

 

Across the two copper rings on the rotor the resistance is 4.4 Ohms and the three white Stator wires are all 0.6 Ohms. What do you think XJ 550H bearing in mind that temperature can affect the readings. Do you think my stator and rotor are ok thanks?

 

your measurements are high and stator out of spec could be your multi meter If you can varify the readings with another meter

Rotor 4.0 ohms +/- 10% for all XJ650, your reading without brushes 4.4. max spec would be 4.4 in spec

Stator 0.46 ohms +/- 10% for all XJ650, your reading 0.6 ohms max spec would be 0.506 out of spec

your charging voltage is stated at "Voltage at the battery is a little low -- lucky to get to 13.2 volts". this reading is at what rpm?


For all XJ-series models, the maximum available charging output VOLTAGE should be as follows (all values are approximate):

* approximately 500-2000 rpms: 1.8 volts gradually increasing to 14.2 volts
* 2000+ rpms: 14.2 volts up to about 14.8 volts, with a maximum of 14.8 volts

could be you need to replace the brush assembly (making poor contact)
could be you have a bad battery remove it from the bike and put it on a charger then wait 24 hrs and test standing voltage.

you should also do a voltage drop test . meter on battery read voltage .press starter see where voltage drops to.

for stator clean all the connectors with electrical spray inspect crimps for bad crimps or corosion.

 

I would suggest that you clean the grounds.
the motor ground from battery and the frame ground as well as the ground rings that are under the mounting bolts for the ignition coils, dirty grounds can cause this problem.
I would also check the diodes in the voltage regulator.

if there is a radio shack near you buy some 1% or 5% resistors in the range you are testing to check out your meter readings

I could be you just have a bad battery it happens even to new batterys.

 

Thanks for all your help XJ550H I need to buy another multimeter to check as you say. The one I have is not very expensive. I think my battery is suffering from some voltage drop so I better buy a new one. I will work through all the steps you advise to check and see if that fixes it. Was out on the bike tonight but using the same multimeter I had 12.8 volts across the battery terminals with the engine running and when I revved the enging to about 2000rpm the voltage stayed the same. I will upload photos off my phone when I can. The rectifier had broken wires put together with blue crimp connectors someone butchered the wiring before I got the bike. I soldered it and put heat shrink tubing over the wires but I think a new rectifier will be needed also. I will try and upload the photos of the rectifier in the next few days. I did not stay out on the bike long as the ignition has died on me twice and I don't want to push the bike home again.

 

Hi XJ 550H lol here is the problem causing my alternator not to work. I had the alternator plugged into the wrong connector on the wiring loom I am now getting proper voltage at the brush connected to the brown wire. Sometimes I don't check the obvious when I was getting no current at the brush dispite checking the brown wire at the fuse box and the switches I noticed the plug from the brushes was in the wrong loom connection. Well better than needing an alternator eh.